A brush motor typically includes a stator and a rotor. The rotor includes a shaft, a rotor core fixed on the shaft, a commutator fixed on the shaft adjacent the rotor core, and rotor windings wound about the teeth of the rotor core and electrically connected to the commutator. The stator includes stator magnetic poles, power terminals and at least a pair of brushes in sliding contact with segments of the commutator. External power is supplied to the rotor windings via the power terminals, the brushes and the commutator. When electrified, the rotor windings form rotor magnetic field which interacts with stator magnetic field to drive the rotor to rotate.
During commutation, when a brush leaves a segment of the commutator, the current passing through the corresponding rotor winding changes abruptly, thereby generating a large induced electromotive force and a strong electric field across an air gap between the brush and the segment. The air around the brush and the segment may be ionized under the strong electric field to form a discharge path and generate sparks. The spark may damage the slide contact between the brush and the commutator, which increases the worn of the brush and the commutator. Hence there is a desire for a commutator with diminished spark.